Photoemissive tube tester



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fly 19 United States Patent O PHOTOEMISSIVE TUBE TESTER Milton Adelman,Robert W. Burke, and Reuben Leibowitz, New York, N. Y.

Application June 10, 1954, Serial No. 435,948

9 Claims. (Cl. S24-29) (Granted under Title 35, U. S. Code (1952), sec.266) The invention described herein may be manufactured and used by orfor the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

This invention is directed to a photoemissive tube tester and moreparticularly to a portable universal photoemissive tube tester operableby a non-technical operator.

There is no universal photoemissive tube tester in the prior art. In thepast, separate setups for each tube type have been used for testingphotoemissive tubes in the factory, warehouse and service shop.

The term phototube is hereinafter substituted for photoemissive tube.

This invention is adapted either for testing different types ofphototubes at discontinuous intervals, or for continuous mass testing oftubes olf a production line, or for mass testing of tube stocks in awarehouse, to determine Whether or not there are any tubes in thewarehouse that have been so adversely affected by shelf life as to nolonger be capable of functioning properly. Of the several measurablephototube characteristics, the anode current is the sole criterion fordetermining the end of useful life for all vacuum and phototubes exceptfor photomultiplier tubes. Even in the case of photomultiplier tubesWhere the amplification characteristic is important, the anode currentfurnishes a reliable indication of the end of useful photomultipliertube life. The effects of shelf life are manifest in a decreased anodecurrent. A measurement of this characteristic is a basic method fordetermining the life stage of all phototubes. In other words, when anodecurrent level of a phototube operating under recommended conditionsdrops below a predetermined reference value the phototube will notfunction properly for the prescribed length of time. lts effective lifeis too short and therefore is unacceptable. This minimum current isascertainable from published Government and commercial specificationsand empirical data and is not discussed herein since it is not germaneto this invention. As for other parameters, life-test studies conductedindependently by scientific personnel at phototube and optical companiesproduced concurring results in that spectral response does not varysignificantly with age. Though results are inconclusive concerning theetfect of age upon dark current, experimentation in Material Laboratory,New York Naval Shipyard, under cognizance of inventors, has shown thatshelf life causes no prohibitive increase in dark current in phototubes.

The tester includes a black box for housing a standard lamp and thephototube under test. The standard lamp is the light source. It operatesat a lixed color temperature and generates a known amount of light flux.

A partition having an aperture is mounted in the black box between thestandard lamp and the phototube under test. The partition serves as abaffle. A mounting plate having an aperture is mounted in the black boxbetween the partition and the phototube under test. A disk having aseries of apertures some of which are covered by neutral density filtersis mounted on the mounting plate. Selected apertures in the disk areadapted to be aligned with the aperture in the mounting plate byrotation of the disk relative to the mounting plate. The sizes and theshapes of the apertures in the mounting disk correspond in each case tothe portion of the cathode of the respective phototube type that isnormally excited by luminous ux under recommended operation conditions.The radial distance between each of the apertures in the disk and thecenter of rotation of the disk, is directly related to the position ofthe cathode of the corresponding phototube under test when the latter isseated in the black box.V Neutral density filters are included `in someof the apertures of the disk for reducing the luminous flux for certainphototube types. The black box further includes master sockets connectedin a test circuit. The phototube under test is adapted to be mounted inproper position in the black box through the use of correspondingadaptors which properly connect the phototub'es with selected terminalsof the master sockets and correctly position the various types ofphototu'bes in the black box relative to the appropriate aperture andstandard lamp. The tester further includes a circuit for applying theoperating potentials to the phototube under test and a meter circuit forindicating the level of anode current. Since the range of anode currentsfor phototubes extends from about .2 microampere to about 200microamperes, the anode current cannot be measured directly by aDArsonval galvanometer. The meter circuit includes a ,self compensatingdirect current amplifier with a variable input shunt. 'the testerfurther includes a phototube power supply. The power supply has tooperate with good regulation since the anode current of gas phototubesand the anode current of multiplier phototubes change greatly with aslight change in operating potentials. The power supply included in thetester is a series regulated power supply which regulates With respectto line and load variation. A control panel is associated with thetester circuitry for conditioning the circuit to `test each of thediiferent types of phototubes. The setting of a minimum number ofcontrols according to a `chart provided right on the test panel,conditions the circuit for testing a particular photo tube. The chartgives the disk position and designates the appropriate adaptor. Theadaptors `are stocked in the tester. Indicator bulbs strategicallyconnected advise as to the opcrability of the circuit. A galvanometer inthe meter circuit and mounted on the panel gives the results.

An object of this invention is to provide a phototube tester.

A further object is to provide a universal phototube tester.

A further object is to provide a `universal -phototube tester whichtranslates test results directly and decisively.

A further object is to provide a universal phototube tester which is'operable by non-technical personnel.

A further object is to provide a universal phototube tester which isportable.

A further object is to provide a universal phototube tester in a singleself-.contained unit.

A further object is to provide a universal phototube tester which isoperable .by non-technical `personnel which is absolutely safe foroperating personnel.

A further object is t-o provide a black `box for use in testingphototubes.

A further object is to provide a black box for use in testing a varietyof types of phototubes.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings wherein:

Fig. l is a perspective view of a preferred embodiment of this inventionwith its various closures in open position,

Fig. 2 is a rear view of the embodiment of the invention shown in Fig. 1with the closures in closed position,

Fig. 3 and Fig. 4 are perspective views of the preferred embodiment ofblack box included in this invention,

Fig. 5 is a plan view with portions broken away of the disk arrangementused in the black -b-ox of Figs. 3 and 4,

Fig. 6 is a cross-sectional view taken along the line 6-6 of Fig. 5,

Fig. 7 is a plan view of the shutter and cam arrangement used in theblack box of Figs. 3 and 4 and is taken from the rear of Fig. 5,

Figs. 8-11 are portions of composite schematic wiring diagram of thetest circuit included in a preferred Vembodiment of this invention,

Figs. 12-19 are simplified schematic wiring diagrams showing theresultant circuit connections for various test conditions, and

Fig. is a chart showing relationship between the tube type under test,the positions of the switches in the disclosed embodiment of theinvention, and the figure numbers corresponding to the switch positions.

The tester 12 is a single self-contained unit mounted in a housing 14.The housing 14 includes a hinged closure 16 supported when in openposition by a folding bracket 18. Handles 22 and 24 are provided on theclosure and sides of the housing 14, respectively. The body 26 of thehousing 14 is subdivided into two portions by a partition 28. On oneside of the partition 28 is mounted a removable black box 32. Thecircuitry portion of the tester is mounted on the other portion and iscovered by an operators panel 34. In the hinged cover 16 of the housing14 is provided another cornpartment 38 for housing a variety ofadaptors. A hinged cover 36 is' adapted to close the compartment 38.Also included in the cover are two other compartments 42 and 46 forstoring standard lamps 44 and for storing a standard phototube 48,respectively. The rear of the housing 14 (Fig. 2) is cut out at 52 and54. Perforated screens 56 and 58 are secured in `the cut-out portions.The screens permit air to circulate through the tester portions to limitthe temperature rise.

The black box 32 is preferably made of Wood. A cover 62 is fastened tothe black box 32 by means of a piano hinge 64. A piano hinge is usedbecause it is important that the cover 62 close the black box 32accurately and therefore completely to aord a light tight enclosure.Latching means for the cover 62 includes a spring clip 62A fixed to thecover 62 and a pin 62B xedto the black box 32 for cooperation -With thespring clip 62A. A rim 66 appends from three sides of the cover62 andwhen the cover is closed the rim 66 embraces the sides of the black box32. -All inside surfaces are painted dull black with a matte nish. Oneend of the black bo-x 32 is partitioned to provide a lamp compartment68. The end wall 72 of the black box which is also the end wall of thelamp compartment 68, is cut out at 74 (Fig. 4). The cut-out 74 is closedby a Ventilating screen which comprises a pair of spaced plates 76 and78 (Fig. 4 and Fig. 3), each of which has apertures for circulating air.The apertures in the spaced plates 76 and 78 are staggered to preventlight from leaking into the black box. Both plates 76 and 78 are paintedblack. A lamp socket 82 is mounted on a pedestal 84 adjacent the endwall of -the box 72. The op posite end of the lamp compartment 68 isbordered by the partition 86 formed with an aperture 88. Both thepartition 86 and the pedestal 84 are designed so that the lamp iilamentis in alignment with the aperture 88 relative to the bottom of the blackbox. A lug 92 is fastened to the top of the partition 86. A cover 94 ispivotally secured to vthe end wall 72 of the black box 32 by means of apiano hinge 96. The cover 94 is 4 adapted to rest on the lug 92. Afinger grip 98 for the cover 94 is' secured to the cover 94 through heatinsulating material. This permits an operator to open the cover 94 evenafter the lamp has been lighted for a period of time suflicient to causethe compartment 68 to become hot.

The metal partition 86 and the metal cover 94 uniformly dissipate theheat given off by the lamp. Additional heat is dissipated through thetwo metal plates 76 and 78 containing the Ventilating holes which arestaggered to provide sufficient circulation of air while retaining thelight-tight qualities ot" the box. The ymetal cover 94 serve-s toprotect the operators eyes from the glare of the lamp when the cover 62of the black box 32 is raised. The metal partition 86 of the lampcompartment 68 serves as a light batiie and permits only direct raysfrom the lamp to pass on to the phototube under test.

A pair of master diheptal sockets 102 and 104 are secured toward theopposite end of the black box 32. The master socket 104 is axiallyaligned with the aperture 88 in the metal partition 86 and the filamentof the lamp mounted in the lamp socket 82. The axis of the master socket182 is perpendicular' to the axis through the -mastet socket 104 and iscoplanar therewith. The master `socket 162 is adapted to be used for allphototubes except end-on phototubes. Endon phototubes are adapted to bemounted in the black box by means of master socket 104. The mastersockets 102 and 184 are wired in parallel. The wiring from the mastersocket 104 extends to the underside of the box by means of an enclosedchannel 106. An alligator clip 108 is fastened in the black box 32adjacent to master socket 182 for completing connections to phototubeshaving either anode or cathode caps. A transverse mounting plate issecured in the black box between the lamp compartment 68 and the mastersockets 102 and 104. A rotatable disk 114 is mounted on one side of themounting plate 112. A shutter and cam arrangement 117 is mounted on theopposite side of the mounting plate 112 (Figs. 5-7). The disk 114 isformed with an `outer ange 116. It is centrally formed with boss 118terminating in substantially the salme .plane as that defined by the endof the outer flange 116. The disk 114 is centrally formed with anopening 122 extending through the boss 118. The surface of the diskopposite the boss 118 is recessed at 124. A plurality of apertures, somerectangular and some circular, are formed in thc disk 114. The aperturesditier in area and radial position. Twin rectangular openings 126 and128 are for phototubes having twin cathodes. The mounting plate 112includes a single rectangular aperture 132. The aperture 132 in themounting plate 112 is axially aligned with the aperture 8S in thepartition S6 and with the filament of the standard lamp in the lampcompartment 68. A cam 134 having a single high point is mounted on theinside of the flange 116 4of the disk 114. The high point of the cam isaligned along a diameter of the disk with the center of the largestrectangular opening of the disk 114 (Fig. 3). The disk 114 is mounted onthe `mounting plate 112 in combination with a shutter and camarrangement 117; it includes a wheel-like cam 136. The wheel-like cam136 operates in combination with a pair of similar shutter members 142and 144. The wheel-like cam 136 is mounted for rotation relative to asupporting pin 146; the pin 146 terminates at one end in a head 148 andat its opposite end in a threaded portion 152. The very end 0f thethreaded portion 152 of the supporting pin 146 is formed with a springreceiving opening. A slot 154 is formed in the mounting plate 112 forpermitting reciprocal movement of the pin 146 and its wheel-'like camrelative to the mounting plate 112. Wheel-like cam 136 is retained onthe pin 146 by means of nuts 156. A spring post 158 is secured to thebottom of the mounting plate 112 in alignment with the slot 154 formedin the mounting plate 112. A tension spring 162 extends between thesupporting pin 146 and the spring post 158 for biasing the wheel-likecam 136 toward the bottom of the supporting plate 112. The head 143 ofthe pin 146 is adapted to bear against the inside perimeter of the ange116 of disk 114. Reciprocal movement of pin 146 is obtained when brasscam 134, which is fastened to the inside of flange 116, slides under pin146 and lifts it. Both the shutter members 142, 144, and the disk 114are mounted for rotary movement about a single axis. The mounting Ymeans for both the disk 114 and the shutter members 142 and 144 includea flanged bushing 166, an externally threaded member 168 having abearing flange 169 fastened to mounting plate 112 by screws 113 forsupporting the shutter members 142 and 144, a screw 172 threaded intothe flanged bushing 166 for retaining the disk 114 and lianged bushing166 in assembled relationship relative to the mounting plate 112, and aanged nut 174 having a knurled surface for retaining the 'shuttermembers 142 and 14-4 on the periphery of the bearing flange 169 of theexternally threaded member 16S without clamping the shutter membersagainst rotation. The flange of the bushing 166 seats in the recess 124iin the outer surface f the disk 114. The bushing 166 extends through anopening 112@ formed in the mounting plate 112. The flanged bushing 166is internally threaded at the end of the bushing opposite the flange.The externally threaded member 168 which is screw-fastened to themounting plate 112 provides a clamping surface for screw 172threadedinto the end of the bushing 166 for retaining the disk 114 andflanged bushing 166 assembled to the mounting plate 112. The peripheryof bearing liange 169 of the externally threaded member 168 is formedwith a finished surface and is located against the surface of themounting plate 112. It supports for rotation the shutter members 1&:2and 144. The bearing flange of the externally threaded member 168 isslightly wider than the combined thickness of the shutter members 142and 144. The shutter members 142 and 144 are retained on the bearingflange 169 of externally threaded member 168 by the knurled nut 174threaded on to the threaded portion of the externally threaded member168 until it abuts the bearing liange. The shutter members 142 and 164are provided with ysprlng-suppo-rting posts 176 and 178, respectively. Atension spring 132 extends between the spring supporting posts 176 and173 for biasing the shutter members toward aperture restrictingposition.

Indexing detent means 180 is secured to the mounting plate 112 forcooperation with the disk 114. The indexing detent means 130 includes aspring housing 182 internally threaded at one end and internally reducedat the opposite end. The spring housing end is internally reduced and isformed with an external flange whereby it is adapted to be clamped tothe mounting plate 112. The mounting means for indexing detent means 180includes a bar 184 drilled and counterbored to seat the liange of thespring housing 182. The bar 184 is screw fastened to the mounting plate112. A compression coil spring 185 and plunger 186 are retained in thespring housing 182 by a set screw 187. A countersunk opening 183 isformed in the mounting plate to be in axial alignment with the indexingdetent means 180 at assembly. At assembly, a steel ball 189 is includedbetween the spring-biased plunger 136 and the mounting plate 112. Theend surface of the ange 116 of the disk 114 is formed with a series ofspaced recesses 190 for seating the spring-biased steel ball of themdexing detent means 130. The recesses in the flange 116 are correlatedwith the openings formed in the disk 114 so that a selected opening inthe disk 114 is positioned in registration with the rectangular aperture132 of the mounting plate 112. Indicia 192 (Fig. 3) are etched into thesurface of the flange 116 of disk 114. The indicia 192 in combinationwith indexing detent means 180 affords a convenient means for settingthe disk 114. The outer surface of the ange 116 is knurled to aiford afinger grip for rotating the disk from one indexed position to anotherindex position. `The openings formed in the disk 114 correspond to thoserecommended by the manufacturer for actual operating conditions.

In the black box 32, the candle power of the standard lamp 82 is xed.Likewise, the distance from the standard lamp to the aperture or openingin the disk 114 is fixed. Therefore, the luminous flux measured at thedisk aperture is a constant. The areas of the various openings in thedisk 114 which are not covered by a lter determine the amount ofluminous ilux incident upon the cathode of the phototube under test. Allthe luminous ux passing through a disk opening impinges upon the cathodeof the phototube under test. As previously stated, the design of theopenings inthe disk 114 correspond to manufacturers recommendations asto actual operating conditions. It is further noteworthy that mostphototubes operate with substantially the same luminous flux, which isgenerally 0.1 lumen. Furthermore, the luminous' liux of 0.1 lumen isgenerally the upper limit for al1 phototubes. Therefore with theapertures size lixed and the desired luminous ux fixed, it is a matterof design, based on practical considerations, as to the candle power ofthe standard lamp and the distance of the standard lamp from the diskopening. Overall blackbox size determines the practical upper limit ofthe distance between the standard lamp and the disk openings. Heatdissipation problems determine the upper limit of the intensity of thestandard lamp. One satisfactory practical embodiment determined fromactual laboratory test has been found to involve the use of acoiled-tungsten, lime-glass envelope lamp operating at a colortemperature of 2870 degrees Kelvin to provide a 50 candle power sourceat a distance of 9.9 inches away from the apertures in the disk 114.This luminous intensity of the standard lamp source and this shortdistance between the standard lamp source and the phototube under testpermits the use of a small light-tight box while at the same timesecuring essentially parallel rays by means of the baffling afforded bythe partition 86 and the mounting plate 112. Because the recommendedluminous flux values for the remaining small percentage of types ofphototubes range downwardly from 0.1 lumen to 0.00001 lumen some of theapertures in the disk are covered by neutral density filters asdescribed below. Generally, all the apertures in the disk 114 are formedsymmetrically with respect to a single circle about the axis of rotationof the disk 114. The exception, that is, those apertures that are at asmaller radial distance from the axis of rotation are so located forpractical considerations in order to limit the necessary number ofadaptors while at the same time causing the luminous llux to impingeupon the central portion of the cathode of the phototube under test.

The rectangular aperture 132 formed in the mounting plate 112 is atleast as large as the largest aperture formed in the disk 114. Adiliculty is encountered when the disk is positioned so that the smalleror smallest aperture in disk 114 is aligned with the rectangularaperture 132 of the mounting plate 112. Luminous flux from the standardlamp leaks through apertures to either side the smallest aperture sincethe rectangular aperture 132 of the mounting plate 112 is so much largerthan the smaller or smallest aperture in the disk 114. `To avoidinaccuracy resulting from luminous flux leaking through non-selectedapertures of disk 114, the shutter members 142 and 144 act to limit thesize of the rectangular aperture 132 of the mounting plate 112 for alldisk positions except that which aligns the largest disk aperture withthe rectangular aperture 132. The shutter members 142 and 144 are heldnormally closed by the tension spring 181 extending between the posts176 and 178 on the shutter members. A pin 143 on. the mounting` plate112 cooperates with shutter member 142, `acts as 7 a stopto define theclosed position nof the shutter members. When the disk is positioned sothat its largest aperture is in operative position, the cam 134 on thedisk 114 forces the supporting pin 146 for the wheellike cam 136 upwardcausing the latter to force the shutter members 142 and 144 apart (Fig.7).

Where the recommended luminous iiux for the phototube under test islower as described previously, a neutral density filter is mounted theaperture of the disk 114. By using neutral density filters secured inparticular disk apertures the tester operation is simplified becausethere is no need for changing the candlepower of the standard lamp orfor varying the distance between the standard lamp and the phototubeunder test. The filtering characteristics of commercially availableneutral density filters vary markedly over the spectral range of thephototubes. A satisfactory type of neutral density lilter for use inthis invention may be formed from several sheets of fresh photographiclm exposed to light for short periods of varied duration. Thetransmission factors of the exposed lm can be determined at a precisionof plus or minus 1% using a galvanometer and a photronic cell. Sinceneutral density filters formed and calibrated accurately in this mannermay still show slight differences in percent transmission at differentportions of the spectrum the anode current of phototubes such assensitive photomultipliers having diverse spectral responses could beaffected. Variations in the anode current due to the spectral responseof the neutral density filter may be measured in the laboratory and maybe compensated for in the metering circuit.

The design of the disk 114 with its various apertures, some of whichhave neutral density filters, is determined by the requirements of thetester. For example, the disk may be made larger to include a largervariety of apertures or it may be made smaller to include a lesservariety of apertures depending upon the operating requirements of thetester. In any case, departure from the basic description is only amatter of design and lies within the purview of those skilled in theart.

The adaptors stored on the hinged cover 36 of the housing 3S areillustrative of the different types needed for correctly positioning thecathodes of respective phototubes in proper test position in the blackbox 32. Besides properly positioning the respective phototubes theadaptors also transfer the proper operating voltages from the testcircuit to the phototubes tested. The adaptors are mounted in thediheptal master sockets 102 and 104. For special tubes having anodecaps, or cathode caps, the operating potential is obtained through theuse of an alligator clip 108 in the black box 32.

- An interlock switch 202 is mounted in the black box for cooperationwith its cover 62. The interlock switch operates to prevent injury topersonnel and damage to any phototube under test. When the cover 62 isopened the interlock switch 202 is adapted to cut off the operatingvoltage(s) from the phototube under test. The interlock switch 202serves the additional purpose of insuring against light leakage into theblack box 32 during a test by preventing operating potentials from beingapplied to the phototube under test until the cover 62 is completelyclosed. This is accomplished by using a sensitive snap-acting switchaccurately positioned within the black box 32. The black box 32 isseated in the housing 14 of the tester 12 in the manner shown in Fig. l.The black box 32 may be modified by elongating it to include asucceeding mounting plate 12 with its associating elements and asucceeding master socket. By this arrangement, the distance between thesource and the phototube under test need not be limited to one fixedvalue. In such a modification, intervening mounting plates could serveas baies.

The test circuit of the phototube tester 12 is included inthe right-handportion of housing 14 and is controllable from the operators panel 34.The test circuit is adapted to be connected to an alternating currentpower supply 220 by way of the terminal 222 at the back of the housing14(Fig. 2). An interlock switch 224 is connected in series with one inputterminal 222 and is physically positioned within the housing 14 so thatif the operators panel 34 is opened for access to the circuitry, thepower supply to the test circuit is interrupted. A double-polesingle-throw switch 226 is connected immediately beyond the interlockswitch 224 in the input power supply circuit. The switch 226 is anon-otl` switch'for the test circuit and is located on the operatorspanel 34. A line fuse 223 is connected in one of the input power supplyleads immediately beyond the switch 226. The line fuse 28 is shunted bya neon indicator bulb 232 in series with a current limiting resistor234. The neon indicator bulb 232 glows when there is a short circuit inthe test circuit that causes the line fuse 228 to open. The indicatorbulb 232 is located in the little chamber at the top of the operatorspanel 34 (Fig. l). The associated fuse 228 (not seen in Fig. l) islocated in the same chamber adjacent the indicator bulb 232 and allowsfor easy replacement. An additional neon indicator bulb 236 in serieswith a current limiting resistor 238 is connected directly across theinput power supply leads immediately beyond the line fuse 228. When theneon indicator bulb 236 glows, it serves to indicate that power is beingsupplied to the test circuit. The neon indicator bulb 236 is locatednear the top of the operators panel 34 irnmediately adjacent the switch226. lf both indicator bulbs do not glow when switch 226 is closed thepower supply 22% is at fault; if both glow, the test circuit is atfault. The primary winding of a line regulating transformer 242 isconnected directly to the fused input supply line. The line regulatingtransformer 242 is in the lamp power supply. Because it handlesconsiderable power, it generates a great deal of heat in continuousoperation. A cooling source, such as a fan 244, for the transformer 242is connected in parallel with the primary winding of the transformer242. An air stream is directed across the transformer 242 by means offan 244. Circulating cooling air is forced by the fan 244 to liowthrough the perforated screen S6 (Fig. 2) at the back of the housing 14of the phototube tester to protect the transformer insulation fromdamage. A variable autotransformer 246 is connected across the secondarywinding of the line regulating transformer 242. The variableautotransformer 246 has a knob; the knob has a pointer which cooperateswith calibration indicia 248. The knob is accessible on the operatorspanel 34 (Fig. l). A fuse 252 shunted by a neon indicator bulb 254 inseries with a current limiting resistor 256 is connected in series withthe variable tap of autotransformer 246. The neon indicator bulb 254indicates trouble beyond the variable autotransformer 246; it is mountedin the chamber at the top of the operators panel 34. A step-downtransformer 253 such as a filament transformer is connected across theoutput side of the variable autotransformer 246. A standard lamp 262normally stored in the lamp compartment 42 of the housing 14 when not inuse is adapted to be energized by the secondary of the stepdowntransformer 258. The standard lamp 262 is laboratory calibrated toafford the necessary high order of accuracy. Calibration of a standardlamp 262 for use in the phototube tester 12 is correlated with thecalibration markings associated with knob 248 of the variabicautotransformer 246 whereby the lamp 262 operates at the correct colortemperature. When a standard lamp is mounted in the lamp socket 32 ofthe tester, the knob of the variable autotransformer is set so that itis aligned with the calibration mark which sets the operating voltageapplied to the standard lamp to that required for use in obtaining theproper color temperature and candlepower from the lamp 262. Replacementstandard lamps 44 are stocked in the phptntube tester as shown in thecompartment 42 of the hollSllg, 14 and are all labeled with thecalibration marking 4for correctly setting the variable autotransformer246.

The test circuit further includes a high voltage power supply 272. Atime delay relay 274 is connected in circuit between the input end `of`the high v oltage power supply 272 and the fused input power line, Thetime delay relay 274 includes a coil 274g adapted to be connected acrossthe fused input power line after a predetermined time delay byconventional means, not shown, The relay includes a pair of contactors2741) and ,274e and corresponding iixed contacts 274d and 274e.` Whenthe coil 2740: is energized the input terminals 2,73 are con,- nected tothe fused input .power line through the contactor 274C and Contact 274eof the time vdelay relay 274. The contacter 274b and the xed contact274b are in the circuit which supplies the anode `voltage to the tubeunder test and is more completely desscribed in succeeding paragraphs. l

The high voltage power supply 272 includes a stepup transformer 276providing an output voltage on the order of 1600 volts to provideoperating potentials up to at least 1000 volts required byphotomultipliers. The primary winding of the step-up transformer 276 isgrounded to the chassis of the ltest circuit. A fuse 278 is connected inseries with the secondary of the step-up transformer 276. The fuse 278-is -shunted by a neon indicator bulb 232 in series with a currentlimiting resistor 284 for advising when there is trouble inAhigh-voltage power supply 272. The neon indicator bulb 282 and the fuseare located in the chamber at the back of the operators panel 34 (Fig.1). A `bridge rectier286 ,is `connected to the secondary of transformer276; it ,comprises gas-lilled rectifier tubes (e. g. 816) because ofcurrent level and inverse voltage requirements. Four separate lamenttransformers generally shown at 288 are provided for the four gas diodesof the bridge rectifier 286. An RC filter is connected across `theoutput of `the rectifier; it comprises a resistor 292 (e. g. 5,000 ohms)and a condenser 294 (e. g. 4 microfarads). A voltage divider comprisingseries-connected resistors 302 (e. g. 2,000 ohms) and 304 (e. g. 2megohms) are connected in series across condenser 294. The junctionbetween resistors 302 and 304 atords a tap 303. Resistors 3.04 and 302are at a ratio of 100 :1. A voltage regulator tube 306 (e. g. VR 150) inseries with a current limiting resistor 308 is connected across thelilter condenser 294. The `output power is derived at the cathode of abeam power amplifier 312 (e. g. 807). The power output of the beam poweramplifier 312 is applied across a multi-sectional voltage divider`comprising series connected resistors 321, 322, 323, 324, 325, 326, and327 (e. g. 18,000 1,000, 3,000, 14,000, 14,000, 138,500, 11,500 ohmsrespectively). The high voltage power supply 272 is connected as aseries `regulated power supply with the output voltage regulated lwithrespect to line and load variations. Regulation is accomplished byautomatically controlling the bias between the control Vgrid and cathodeof the beam power amplifier 312. `The screen grid of the beam poweramplifier 312 is retained at a substantially constant potential throughav screen dropping resistor 328 (e. g. 35,000 ohms). The bias betweenthe control grid and cathode of the beam power amplifier 312 isdependent upon the amount of `current flow through the plate loadresistor 332 (e. g. 1 megohm) of the pentode control tube 314 (e. g.7C7).` The control grid of the beam power amplifier 312 is connected tothe plate of the pentode control tube 314 through a parasitic suppressorresistor 334 (e. g. 5,000 ohms). The suppressor grid and the cathode ofthe pentode cont-rol tube 314 are held at a constant potential by thevoltage regulator tube 306. The bias on the control .grid and the screengrid of the pentode control tube 314 are ,dependent upon the linevoltage and the load voltage. Flhe bias of boththe control grid and thescreen grid Qftherautotle central tube `31,14

is obtained through a voltage divider including resistors 3 36 333, and342 (350K, 500K and 1.5M ohms, respectively). The bias on both gridsvaries directly with the current ow through the series connectedresistors 338 and 342 of the voltage divider. rlhe current through theseresistors 338 and 342 varies as a function of the potential at thecathode of the beam power amplifier 312 and also as a function of Vthepotential at the tap 303 of the voltage divider connected across thefilter condenser 294. The tap 303 of the voltage d ivider on the lineside of the high voltage power supply 2172 is connected to the tap 337of the voltage divider across the load side of the high voltage powersupply `272. The Vconnecting means between these two taps include achassis adjustable rheostat 344 in series with a resistor `346 (e. g.Y24,000 ohms) for limiting the range of adjustment of rheostat 344. Therheostat 344 is adapted to be adjusted so that the potential at the taps303 and 337 are proportional for a particular level of line and loadvoltages. If either the line voltage or the load Voltage decreases thepotentialon both the screen and the control grids of the pentode controltube 314 goes in negative direction. Conversely, if the line voltage orthe load voltage increases the potential on the control and screen gridsgoes in a positive direction. In either case, there is a coincident butopposite reverse change in the bias of the beam power amplifier 312 dueto the change in the current ilow through the plate load resistor 332.As a result, the load voltage is kept constant. A condenser 343 (e. g..l5 microfarad) for neutralizing ripple voltage is connected between thecontrol grid of the pentode control tube 314 and the cathode of the beampower amplifier 312. A high degree of regulation is essential for properoperation of the test circuit since in the case of gas phototubes and inthe case of photomultiplier tubes, a slight change in the anode voltagecauses a considerable percentage change in anode current. Resistors usedin the high voltage power supply are necessarily accurate.

Each of the taps of the voltage divider connected across the output ofthe high voltage power supply `272 are connected in series withresistors 352, 354, 356, 353, 362, 364, and 366, respectively,corresponding to recommended loadresistors for the different types ofphototubes. The common output terminal at the low end of the highvoltage power supply is not connected in series with any resistor. Eachof the aforementioned resistors act as limiting resistors in the samemanner as under actual operating conditions. Under operating conditionsthe limiting resistors generally serve as a means for limiting currentflow in the event that the electrodes of the phototube become shorted.

A meter circuit 372 is provided for indicating the level of anodecurrent in the phototube under test. The meter circuit 372 includes agalvanometer 374. For test purposes the galvanometer 374 is providedwith a scale having three arcuate color segments. The arcuate segment atthe low end of the scale is labeled bad; the arcuate segment at the highend of the scale is labeled good, and the very small arcuate segmentbetween the two is adapted to `be used checking the test circuit withstandard phototube 48. The galvanometer 374 is calibrated with the aidof a rheostat 376 connected in series with the galvanometer 374. If thetest circuit is operating properly when checked with standard phototube48, the pointer of the galvanometer 374 moves into registration with thecentral arcuate segment of the scale `of the galvanometer 374. If thisdoes not occur the `rheostat 376 is adjusted to give full scaledellection of the galvanometer 374 when a potential of exactly 1.5 voltsis applied to the meter shunt 442. The galvanometer 374 is sliunted by abypass condenser 378. Since the current level to `be measured is in therange extending from a fraction of a microampere up to several hundredmicroamperes, an amplifier is combined with the galvanometer 374. Theamplifier used is a conventional direct current push-pull bridgecircuit.

' 11 The amplifier includes a twin triode 382 (e. g. 12AU7). The plateand filament power for the twin triode 382 is obtained from atransformer 384. The transformer 384 includes a primary winding 386 andsecondary windings 383 and 392. A fuse 394, shunted by a neon indicatorbulb 396 and current limiting resistor 398, is connected in series withone side of the primary winding 386. The neon indicator bulb and faceare located in the chamber at the back of the operators panel 34. Thecombination of primary winding 386 and its fuse and indicator bulb areconnected across the fused input power line. The centertap of thefilament of the twin triode 382 is connected to one side of thesecondary winding 392 and the opposite ends of the filament of the twintriode 382 are connected to the other end of the secondary winding 392of the transformer 384. The plate voltage for the twin triode .382 isobtained from the secondary winding 388. A half wave rectifier 402 inseries with an RC filter including resistor 404 and condenser 406, isconnected across the secondary winding 388. A voltage divider includingseries-connectedv resistors 408 and 412 is connected across the filtercondenser 406. The cathodes of the twin triode are coupled through aresistor 414. Cathode resistors 416 and 418 are provided for respectivesections of the twin triode 382. Corresponding ends of the cathode-resistors 416 and 418 are joined and connected in series with theresistor 422 to the low potential end of the filter condenser 406. Plateload resistors 424 and 426 are provided for respective sections of thetwin triode 382. Balance is obtained at zero input by means of apotentiometer 428. The resistance winding of the potentiometer 428 isconnected between the ends of plateload resistors 424 and 426. Platevoltage is applied to the twin triode 382 through the tap of thepotentiometer 428. By adjusting the tap of the potentiometer 428 untilthe plates of the twin triode 382 are at the same potential, a pointerof the galvanometer 374 is zeroed in. The knob of the potentiometer 428is on the operators panel 34. The tap between resistors 408 and 412 ofthe voltage divider provides the operating bias. Stray pick-up bypasscondenser 432 and 434 are connected in circuit with the Irespectivegrids of the twin triode 382. A grid resistor 436"is connected incin-cuit with the grid of the reference section of the twin triode 382.The resistor connected in circuit with the input section of the twintriode 382 includes a fixed resistor 438 and a variable resistance 442(e. g. decade box). Variable resistor 442 serves as a meter shunt foradjusting the range of the meter circuit. The meter shunt 442 includesfour separately adjustable knobs 444, 446, 448, and 452 on the operatorspanel 34. By adjusting the resistance of the meter shunt 442 for thedifferent phototubes so that 2/5 scale deflection is obtained for theminimum acceptable anode currents encountered in the differentphoto-tubes, the result of the qualitative reading may be taken off thesingle galvanometer 374. Meter circuit 372 is adapted to be connected inseries with the `cathode of the phototube under test in all cases exceptwhen multiplier phototubes are tested. By connecting the meter circuit372 in the cathode side, the -circuit is subject to less stray effect.Furthermore, it is preferable to have operating components at the lowestpossible potential.` However, in the case of multiplier phototubes,cathode current is not identical with the anode current because ofdynode currents. Therefore, it is necessary to connect Vthe metercircuit 372 in series with the anode of multiplier phototubes. Pluralswitch means as described below serve to perform this function.

A pair of plural switches, 454 and 456, serve to properly condition thetest circuit in accordance with the phototube to be tested. Generallythese plural switches 454 and 456 serve two primary functions. One ofthe functions is to select among the range of voltages obtainable fromthe high voltage power supply 272 for application to the anode of thephototube under test. The other function is to connect the meter circuit372 in series with r12 either the anode or the cathode of the phototubeunder test in accordance with whether or not the phototube under test isa multiplier phototube, as described above. The switches 454 and 456control the application of the proper voltage to the phototube undertest by controlling the potential applied to the terminals of the mastersocket 102 or 104. A properly designed adaptor selected from thosestocked in the hinged cover 16 of tester 12 mounts the phototube undertest in the master socket. It supports the phototube in correct positionrelative to the disk opening and also transfers the operating potentialto the phototube.

The plural switch 456 is an eight position, six deck switch. The pluralswitch 454 is a five position, two deck switch. Two positions of theeight position switch are devoted to multiplier phototubes having twodifferent numbers of dynodes. Two other positions ofthe eight positionswitch are devoted to twin phototubes whereby both sections of the twinphototubes are excited at the same time while the anode current of eachis metered separately. By. switching the contactors of switch 456 intopositions l, and 2, the meter circuit 372 is connected in series withthe anode of a phototube under test; in this case the phototube undertest is a photomultiplier (Fig. 13). In all `other cases the metercircuit 372 is connected in series with the cathode of the phototubeunder test. Large currents are measured in the case of photomultipliertubes and therefore the leakage currents are only a negligiblepercentage of the total current.

The switch 454 applies the voltage selected by the switch 456 to theproper pin(s) of the master socket, and the plate/cathode alligator clip108 in the black box 32.

Whenk testing twin phototubes `(Figs. 14 and 15) the anodes areconnected in common to the high side of the power supply. The cathodecurrent is measured separately for each. i

Switch deck 456A selects the proper anode potential from among the sevenlevels of potential made available by the high voltage power supply 272.The remainder of the switch decks 456B--456F in combination with theswitch decks 454A and 454B of the other plural switch 454 servetofconnect the meter circuit 372, the phototube under test in the blackbox and the selected tap of the high voltage power supply 272 in propercircuit relationship for the various types of phototubes being tested asshown in Figs. 12-19.

Fig. 20 shows a generalized chart listing six basic breakdowns ofphototube types and the positions of switches 454 and 456 correspondingto each of the six tube types. More particularized information isobtainable from a tube chart mounted on the operators panel 34. The tubechart on the operators panel 34 lists for each of the particular tubesadapted to be tested by the phototube tester 12 the position of the disk114 in the black box 32 as indicated by the indicia 192, the particularadaptor to be selected from the adaptor compartment 36 for properlypositioning the phototube and completing the necessary electricalconnections between the phototube and the master socket 102 or 104 inthe black box 32. The particular master socket to be used (102 or 104)is also indicated by the chart. The proper setting of the meter shunt442 is obtainable from the chart where the chart indicates the positionsof each of the knobs 444, 446, 448, and 452. The positions for switches454 and 456 are likewise indicated on the chart. By means of thisinformation it is a simple matter to condition the tester for testingany particular tube within the range adapted to be handled by thetester. A standard phototube 48 is provided for checking the phototubetester 12 and the standard lamp 44. With the proper settings of theseveral variables the pointer of the galvanometer 374 comes intoregistration with the central arcuate portion ofthe galvanometer scaleif the tester and the standard lamp are operating properly. If suchisnot the case, the standard lamp is changed and the tester 12 is againtested with the standard phototube 48. By this arrangement, it ispossible to constantly keep check of the accuracy of the phototubetester 12.

The tester is constructed and arranged so that anode voltage is notapplied to the tube under test until the black box is closed and apositive switching operation is performed by an operator. This affordsthe necessary measure of safety both to the operator and to thephototube under test. This function is performed in part by means of arelay 472 including relay coil 472er, contactors 472b and 472C and fixedcontacts 472b and 472e. The relay coil 472a is adapted to be energizedfrom the fused input power line. Assuming the conditions are such thatthe interlock switch 224 on the chassis is closed, the on-off switch 226on the operators panel is in closed position and the time delay relay274 has had time to become energized so that the contactor 274b is inengagement with the xed contact 2740?, the circuit is conditioned sothat the relay coil 472er may be energized. However, before the relaycoil 472a can be energized, it is necessary to close the cover 62 of theblack box 32 so as to close the interlock switch 202 in series with therelay coil 47211. The only condition remaining to be satisfied beforethe relay coil 472 becomes energized, is that the push-button switch beactuated by the testoperator. The switch 474 is operated from theoperators panel 34. When the push-button switch is pressed to closedposition, if all the positions precedent outlinedV above are satislied,the relay coil 47252 becomes energized causing the contactor 472b toengage the fixed contact 472d and the contactor 472C to engage the iixedcontact 472e. In order that the test operator may know whether or notanode voltage is being applied to the phototube under test when thepusln button switch 474 is actuated, an indicator bulb 476 in serieswith a current limiting resistor 478 is connected across the fused inputpower line when the contactor 472e engages the xed contact 472e to applyanode voltage to the phototube under test. The neon indicator bulb 476is located on the operators panel 34 immediately above the push-buttonswitch 474.

In operation, the phototube tester 12 is brought to the site of the testand is seated on a bench so that the cabinet is horizontal. A line-cord,not shown, is adapted to connect the input line terminal 222 of thephototube tester 12 to a source of alternating current power 220 such asan ordinary lighting circuit. The hinged cover 16 of the tester 1.2 isswung into open position and braced by a folding bracket 18. Thephototube test circuit is conditioned for operation by throwing theoperating member of the switch 226 to on position. The neon indicatorbulb 236 glows if power is being supplied to the circuit. As soon as theswitch 226 is actuated, fan 244 is caused to rotate to circulate coolingair through the perforated screen 56 at the back of the housing 14. Astandard lamp is selected from the compartment 42 in the hinged cover 16of the housing 14. The lamp is inserted into the lamp socket 82 in thelamp compartment 68 of the black box 32. The lamp power supply isproperly adjusted by setting the pointer knob of the variableauto-transformer 246 to that calibration marking on the panel 34Vcorresponding to the number indicated `on the container of the standardlamp selected for use. With the lamp supply properly adjusted, the lampis energized to the proper color ternperature and candlepower for whichthe tester 12 is designed. The cover 94 of the lamp compartment 68serves to keep light from the lamp out of the test operators eyes sincethe lamp is energized as soon asthe switch 226 is actuated. A standardphototube 4S is available in the compartment 46 for determining whetheror not the tester 12 is operating properly. Information for setting upthe circuit and the black box for use with the standard phototube 4S isdetermined from the tube chart at the front of the operators panel. Anadaptor for the standard phototube is selected from the adaptorcompartment 36` and is inserted into a master socket 102 of the blackbox 32. The standard phototube is the inserted into the adaptor. Thedisk 114 in the black box is turned to proper position when the indicia192 on its ange is in accordance with the tube chart. The black box isthen in condition for operation. The cover 62 of the black box 32 isthen closed which further acts to condition the remainder of the testcircuit for operation by actuating the interlock switch 201 whichpermits application of anode voltage to the phototube in the black box32. The` meter shunt is adjusted by setting the knobs 444 446, 448, and452 on the operators panel to the proper value of meter shuntresistance. The switches 454 and 456 are likewise positioned to therespective settings for applying the proper anodevoltage to thephototube in the black box 32. It is necessary to zero the galvanometer374 prior to any? test. With no current input, the meter is` zeroed byadjusting the knob of the potentiometer 4218 in the meter amplifiercircuit so that the plate potentials of the two triode sections of thedouble triode 382 are made equal. The test circuit is then ready foroperation. The only thing remaining for the operator to do is to pressthe button on the push-button switch 474. If thev circuit is operatingproperly, as soon as the push-button switch 474 is operated, theindicator bulb 476 immediately above the push-button glows. With thecircuit set up for a standard phototube, the pointer of the galvanometer374 moves to the center arcuate portion of the scale if the standardlamp and the remainder of the circuit is operating properly. The sixindicator bulbs on the operators panel 34 advise as to whether there isany trouble in the test circuit and precisely in which portion of thetest circuit the trouble exists. If any of the indicator bulbs 232, 254,284, and 396, located in the chamber at the back of the operators,lpanel 34 being to glow, the operator is notified that the fuse locatedin the particular associated circuithas` become inoperative. Fusereplacement is simplified because the fuse associated with eachparticular indicator bulb is mounted in the chamber at the top of thepanel 34 adjacent the indicator bulbs. If replacement of the fuse doesnot solve the particular trouble, the trouble is localized and itispossible to quickly determine which of the elements is the source of thetrouble. When the push-button 474 is pressed, indication is afforded bythe galvanometer 374 as to the condition of the phototube under test.The procedure for any phototube is similar to that described inconnection with the standard phototube. All the needed information isdetermined from the tube chart. Interlocks both in the black box 32 andthe chassis proper afford needed protection to the operating personnelfrom high voltage generated within the circuit.

Obviously many modiiications and Variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

We claim:

l. A black box for use in testing any of a plurality of Vtypes and sizesof electrical elements which are responsive to radiant energy in andabout the frequency range of visible light, said black box comprising anelongated rectangular box having a hingedly connected closure formingone of the elongated sides of said box, a black nonreiiecting materialcoating the inside surfaces of said box, a pedestal-mounted socket xedlysecured` at one `end of said rectangular box for supporting a :source ofthe radiant energy in a predetermined position in said rectangular boxand for transferring operating power to` a source of radiant energysupported therein, a pair of master sockets secured at the opposite endof said rectangular box, the axis of one of said master sockets beingparallel to the axis of said first-mentioned socket and the axis. of,the other of said master sockets being perpendicular to the axis of saidfirst-mentioned socket, the axes of both master` sockets and of saidfirst-mentioned socket being coplanar, a partition secured transverselyin said` rectangular box and formed with an aperture for permitting apredetermined amount of the radiant energy llux emitted by a source ofradiant energy mounted in first-mentioned socket to pass through, amounting plate formed with an aperture secured in said rectangular boxbetween said partition and said master sockets, the aperture in saidmounting plate being aligned with the aperture in said partition, a diskmounted on one side of said mounting plate, said disk being cut out toprovide arcuately spaced apertures of various configurations and areas,a neutral density filter mounted in at least one of the apertures ofsaid disk, means associated with said disk and said mounting platewhereby said disk is rotatable into any one of a plurality of positionsfor bringing selected apertures therein into registration with theaperture in said mounting plate, shutter means mounted on the side ofsaid mounting plate opposite said disk, cam means mounted on saidmounting plate and associated with said disk and said shutter meanswhereby said shutter means is caused to effectively reduce the size ofthe aperture in said mounting plate when smaller disk apertures arealigned therewith so as to prevent radiant energy ux leakage throughapertures in said disk not aligned with the aperture in said mountingplate and adaptor means for mounting a phototube in one of said mastersockets.

2. A black box as described in claim l wherein said shutter meansincludes a spring for biasing said shutter means toward aperturereducing position, said disk being constructed and arranged to causesaid cam means to automatically move said shutter means out of aperturereducing position for at least one position of said disk.

3. A phototube tester comprising a black box having a closure, astandard lamp mounted in said black box, said black box including meansfor mounting and transferring selected operating potentials to aphototube under test, an interlock switch mounted in said black box incooperative relationship with said closure whereby said interlock switchis closed when said closure is in closed position on said black box, anadjustable lamp power supply connected to said standard lamp, a highvoltage power supi ply providing a plurality of operating potentials, ameter circuit including a galvanometer and adjustable input means forselectively varying the range of said galvanometer, said meter circuitadapted to be connected in series with a phototube under test and withsaid high voltage power supply for indicating resultant phototube anodecurrent, selector means for selecting a particular one of the operatingpotentials aorded by said high voltage power supply for application to aseries combination of a phototube under test and said meter circuit andfor further connecting said meter circuit in series` either with theanode or with the cathode of a phototube under test, said interlockswitch being connected in circuit with said selector means and adaptedto prevent application of operating potential to a phototube under test1until said black box is closed by said closure.

' '4; A phototube tester comprising; a black box having a closure, astandard lamp mounted in said black box; means mounted in said black boxfor mounting and transferring selected operating potentials to aphototube under test; an adjustable lamp power supply connected incircuit with said standard lamp; a high voltage power supply providing aplurality of operating potentials; a meter circuit including a meterconnected to a direct current push-pull bridge circuit ampliiier havingan adjustable input means, said adjustable input means of said metercircuit being adapted for selectively varying the range of said meter,said meter circuit adapted to be connected in series with a phototubeunder test and with said high voltage power supply for indicatingresultant phototube anode current; selector means for selecting aparticular onev of the operating potentials afforded by said highvoltage powersupply for application to a series circuit of a phototubeunder test and said meter circuit, and

further for connecting said meter circuit in series either 16 'with theanode or with the cathode of a phototube under test.

5. A universal phototube tester comprising a black box having a closure,a standard lamp mounted in said black box, master socket means securedinside said black box remote from said standard lamp for use in mountingand transferring selected operating potentials through an adaptor to aphototube under test, luminous ux baling means secured within said blackbox between said standard lamp and said master socket means andincluding means for affording any of a plurality of selected aperturesfor passage of luminous flux from said standard lamp to a phototubeunder test, an interlock switch mounted in said black box in cooperativerelationship with said black box in cooperative relationship with saidclosure whereby said interlock switch is closed when said closure is inclosed position on said black box, an adjustable lamp power supplyconnected to said standard lamp, a regulated high voltage power supplyproviding a plurality of operating potentials, a meter circuit includinga galvanometer and adjustable input means for selectively varying therange of said galvanometer, said meter circuit adapted to be connectedin series with a phototube under test and with said high voltage powersupply for indicating phototube anode current, a pair of independentlyoperable switches for selecting a particular one of the operatingpotentials afforded by said high voltage power supply for application toa series combination of a phototube under test and said meter circuitand for further connecting said meter circuit in series either with theanode or with the cathode of a phototube under test, said interlockswitch being connected in circuit with one of said independentlyoperable switches for preventing application of operating potential to aphototube under test until said black box is closed by said closure, anormally open push-button switch in series with said interlock switchand adapted to be actuated when said tester is readied for operation,and a plurality of indicator means for giving notice as to the operatingcondition of said tester.

6. A universal phototube tester as described in claim 5 wherein saidlight bathing means includes a multiposition disk having a plurality ofapertures, a neutral density lter in at least one of the disk apertures,a mounting plate having an aperture, means for supporting said disk onsaid mounting plate whereby selected apertures of said disk are movedinto registration with the aperture in said mounting plate, said lightbaffling means further including shutter means secured to said mountingplate for effectively reducing the size of the aperture in said mountingplate in accordance with particular positions of said disk.

7. Means for use in testing elements responsive to radiant energy, saidmeans comprising, a box having a closure, a mounting plate, saidmounting plate having an aperture, said mounting plate secured in saidbox intermediate the ends thereof to prevent radiant energy fromtransferring from the portion of said box on one side of said mountingplate to the portion of said box on the other side of said mountingplate except through the aperture, a disk mounted on one side of saidmounting plate, said disk being cut out to provide arcuately spacedapertures of various configurations and areas, means associated withsaid disk and said mounting plate whereby said disk is rotatable intoany one of a plurality of positions for bringing selected aperturestherein into registration with the aperture in said mounting plate,shutter means mounted on the side of said mounting plate opposite saiddisk, means mounted on said mounting plate and associated with said diskand said shutter means whereby said shutter means is caused toeffectively reduce the size of the aperture in said mounting plate whena small disk aperture is aligned therewith so as to pre-

